Slide 1Part 1: Basic Geographic ConceptsSymbolizationVocabularyTerminologySlide 6Slide 7Real World  Data ObjectsReal World  Cartographic ObjectsTopologyConceptualizing TopologyAdjacencyConnectivityContainmentDirectionProximityComplex Case: OverlapPart 2: GIS Data ModelsContinuous & DiscreteSlide 20Continuous & DiscreteContinuous or Discrete?Slide 23Raster Data ModelRaster data examplePart 3: The vector data modelVector Data ObjectsSpatial ObjectsSlide 29Thought question:Thought questions:Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37Slide 38Slide 39Slide 40Slide 4111Spatial Data Models and Spatial Data Models and StructureStructure22Part 1: Basic Geographic Part 1: Basic Geographic ConceptsConcepts•Real world -> Digital Environment–GIS data represent a simplified view of physical phenomena•These data contain:–Locational Information–Non-spatial attributes33SymbolizationSymbolization•In a GIS, we represent real world phenomena in a digital format44VocabularyVocabulary•Real-World Entities or Phenomena•Data Objects•Cartographic Objects55TerminologyTerminology•Entities or Phenomenon -- real world features to be represented in a database66TerminologyTerminology•Data Objects -- digital representations of entities or phenomenaPastureRoadHouse77TerminologyTerminology•Cartographic Objects -- real-world entities as depicted on maps88Real World Real World  Data Objects Data Objects•Attributes–Information about object (e.g., characteristics)•Location/Spatial information–Coordinates–May contain elevation information•Time–When collected/created–Why? Objects may have different attributes over time99Real World Real World  Cartographic Cartographic ObjectsObjects•Real world objects differ in:–Size–Shape–Color–Pattern•These differences affect how these objects are represented on maps•Where possible the cartographic objects (i.e., map symbols) can relate to the entities they are representing (e.g., water = blue)1010TopologyTopology•The spatial relationships between data objects1111Conceptualizing TopologyConceptualizing Topology•Primary–Adjacency–Connectivity–Containment•Secondary–Direction–Proximity (distance)1212AdjacencyAdjacencySpringfieldSpringfieldShelbyvilleShelbyville1313ConnectivityConnectivityThese roads are connected at the black points.1414ContainmentContainmentMoe’sMoe’sKwik-E-MartKwik-E-MartNuclearNuclearPlantPlantSpringfieldSpringfield1515DirectionDirectionMoe’s is Northeast of Moe’s is Northeast of the Kwik-E-Martthe Kwik-E-MartThe nuclear plant is The nuclear plant is Southeast of the Kwik-Southeast of the Kwik-E-MartE-MartMoe’sMoe’sKwik-E-MartKwik-E-MartNuclearNuclearPlantPlant1616ProximityProximityHomer lives near NedHomer lives near NedHomer lives far from Homer lives far from GrampaGrampa1717Complex Case: OverlapComplex Case: OverlapSpringfieldSpringfieldBlue Lake1818•Entities in the real world are represented as one of the following in a GIS:–Raster data•Pixels in an array–Vector data•Points•Lines•Areas (or polygons)Part 2: GIS Data ModelsPart 2: GIS Data ModelsKey concept!1919•“The continuous field view represents the real world as a finite number of variables, each one defined at every possible position. “•“The discrete object view represents the geographic world as objects with well-defined boundaries in otherwise empty space. “Continuous & DiscreteContinuous & Discrete2020Continuous & DiscreteContinuous & Discrete•Some data types may be presented as either discrete or continuous–Example•Population at a point (discrete) •Population density surface for an area (continuous)2121Continuous & Continuous & Discrete Discrete •Continuous –Data values distributed across a surface w/out interruption –Key words: What varies and how smooth? –Examples: elevation, temperature •Discrete–with well-defined boundaries in otherwise empty space–Examples•Points: Town, power pole•Lines: Highway, stream•Areas: U.S. Counties, national parks2222Continuous or Discrete?Continuous or Discrete?www.regional.org.au/au/asa/2003/i/6/walcott.htm2323Continuous & DiscreteContinuous & Discrete•In computer databases –Raster data models represent continuous data–Vector data model are used for discrete objects2424Cell (x,y)The raster data model represents the Earth’s surface as a two-dimensional array of grid cells, with each cell having an associated value:1 2 3 5 84 6 8 3 93 5 3 3 17 5 4 3 92 2 4 5 2Cell valueCell size = resolutioncolumnsrowsRaster Data ModelRaster Data Model2525Raster data exampleRaster data exampleElevation data: each cell contains a number representing the elevation of that cell.2626Part 3: The vector data model2727Vector Data ObjectsVector Data ObjectsGeographic building blocks•Points–0 dimensional •Lines–1 dimensional•Polygons–2 dimensional2828Spatial ObjectsSpatial Objects•Data objects in the vector data model can be:–A point can represent:•Tree, airport, a city, street intersection, a movie theater, a benchmark–A line is a data object, made up of a connected sequence of points. It can represent:•Roads, rivers, regional boundaries, fences, hedgerows, power lines–A polygon is an enclosed area. Examples:•A census tract, Saunders building, boundary of Chapel Hill, a lake, a watershed, a city2929Object example: oak tree3030Thought question:Thought question: How are you going to represent the California OAK tree in digital format?A point? A polygon? Or a pixel?It will depend on:-Scale of observation-Purpose of your research-The type of data you have access to in the GIS3131– When do you want to represent Chapel Hill as a polygon object instead of a point object?– When do you want to represent a river as a polygon instead of a line?Thought questions:Thought questions:3232pointline polygon(area)(x,y)(x,y)(x,y)(x,y) (x,y)(x,y)(x,y)(x,y)(x,y)(x,y)The vector data objects•The vector data model represents geographic features similar to the way maps do–A point: recorded by a pair of (x,y) coordinates.–A line: recorded by joining more than one point, –A polygon: recorded by a joining multiple points that enclose an area(x,y)3333Vector Data Storage in Computers: PointsPointsData Storage+1+2 +3+4Point ID Coordinates1 1, 12 4, 23 6, 2 4 2, 403434(x1,y1)(x2,y2)(x3,y3)②①Line # Coordinates ① (x1, y1) (x2,y2)